An excellent overview article on the different sources of available water appeared in a recent edition of the Environmental Building News (EBN). The article opens by drawing the case for “alternative sources” due to climate change, growing population and current unsustainable groundwater extractions. It then briefly mentions the need for efficiency and the different uses of water (i.e. potable and nonpotable), but then quickly dives directly into the review of the different sources of “new” water (e.g. graywater, rainwater, air conditioner condensation, mechanical equipment blowdown, treated wastewater, and desalination). Each water sources is reviewed in detail and a table summarizes the pros and cons of each.

Some of the key points made in the article include:

Separate plumbing in and around buildings for potable and nonpotable water, opens up significant new options for water supply

Rainwater collection or air-conditioner condensate may be possible to aggregate from several roofs and use common storage to improve their economic viability

The city of San Antonio refers to the combination of condensate recovery and rainwater harvesting as “rainwater plus”

Storing rainwater and condensate recovery in one location makes more economic sense. Condensate production is fairly steady, and increases as it gets hotter, and rain is infrequent and intense; by storing together smaller tanks can be used

Savannah, GA adopted a regulation allowing graywater to be used for toilet flushing

Volcano, HI depends entirely on rainwater for its water supply

In large commercial buildings, condensate recovery often produces enough water to supply all of the irrigation needs

Desalination is well suited to solar-thermal power plants, due to its energy intensive nature and this approach also addresses some of desalination's negative environmental impacts

The article provides a chart comparing the energy intensity for differing sources of waters for San Diego, CA. Reclaimed wastewater is the least energy intensive, while desalination is the most. Unfortunately, rainwater harvesting was not included in the comparison at all.

The article also includes a table depicting the various graywater regulations around the country. It is apparent based on the table only a handful of locales are actively pursuing graywater as a source today, but hopefully others will soon follow. It specifically calls out Malibu, CA as having a handbook on implementing a graywater system including design criteria for both large and small systems as a good source of information.

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